Touch Electrode Sensing Circuit for RF Noise-Resistant Detection

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Solution Overview

Problem

Existing touch sensor devices face inefficiencies in signal acquisition and are prone to erroneous detection due to interference noise and radiation issues, particularly when mounted on RF communication chips like Bluetooth low energy chips.

Innovation Solution

A touch sensor device incorporating a driver unit that uses a voltage with a triangular waveform to drive the touch electrode, a monitor unit to track drive current, a rectifying unit for full-wave rectification, and a smoothing unit to convert the rectified current into a signal corresponding to capacitance, along with a phase adjustment unit to manage noise cancellation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a conventional touch sensor device uses an oscillator to detect capacitance changes, then the touch state can be detected, but the oscillation frequency is susceptible to interference noise and environmental factors causing erroneous detection

Engineering Contradiction:

Improvetouch detection accuracyVSAvoiddetection reliability

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent replaces the oscillator-based detection system with a capacitor charging system. Instead of measuring oscillation frequency changes, the system charges the touch electrode capacitor through a known resistance and measures the charging time. This substitution eliminates the susceptibility to oscillation noise and environmental interference, providing more reliable touch detection.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces a known resistance as an intermediary element in the charging circuit. By measuring the time required to charge the touch electrode capacitor through this known resistance, the system can calculate capacitance changes without directly measuring the capacitor itself, thereby isolating the measurement from interference noise and improving detection reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If a switched capacitor is used to convert capacitance to current, then erroneous detection can be prevented, but the efficiency of acquiring signals is low

Engineering Contradiction:

Improvedetection reliabilityVSAvoidsignal acquisition efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent implements continuous charging of the touch electrode capacitor through a known resistance, rather than using discrete switched capacitor operations. This continuous charging process allows for more efficient signal acquisition while maintaining detection reliability, as the system can continuously monitor the charging progress and detect touch events without the inefficiencies of periodic switching operations.

Inventive Principle:

Principle #20Continuity of useful action

3Adaptability or versatility

If the touch sensor device is mounted on an RF communication chip, then integration is achieved, but radio waves can enter the touch electrode as disturbance noise or interfere with RF reception

Engineering Contradiction:

Improvedevice integrationVSAvoidradio wave interference

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent extracts the touch sensing function from the RF communication chip by implementing a separate charging circuit using a known resistance. This separation allows the touch electrode to be charged through a controlled resistive path rather than through the RF chip, thereby preventing radio wave interference from entering the touch electrode or disrupting RF reception while maintaining integration benefits.

Inventive Principle:

Principle #2Taking out (Extraction)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This configuration enhances signal acquisition efficiency, reduces radiation noise, and effectively cancels disturbance noise, improving detection accuracy and reducing the size of touch buttons while minimizing radiation interference.

Implementation Method 1

a rectifying unit that performs full-wave rectification of the current monitored by the monitor unit

Methodology Applied

Scientific EffectFull-wave rectification: Diode

Implementation Method 2

a smoothing unit that smooths the rectified current and converts the rectified current to a current that corresponds to the capacitance of the electrode

Methodology Applied

Scientific EffectCapacitive filtering: Capacitance

Data Source

PatentUS12130158B2Touch sensor device and electronic device equipped with touch sensor device

Publication Date: 2024.10.29 SONY SEMICON SOLUTIONS CORP

AI summary

The present disclosure provides a touch sensor device that can improve efficiency of acquiring signal components and that can effectively address noise and electromagnetic interference. The touch sensor device includes a driver unit that drives an electrode having a capacitance that changes due to contact, using a voltage having a waveform of any shape, the voltage gradually changing from a first voltage value that is higher than a reference voltage to a second voltage value that is lower than the reference voltage, and from the second voltage value to the first voltage value, a monitor unit that monitors a drive current obtained by driving the electrode, a rectifying unit that performs full-wave rectification of the current monitored by the monitor unit, and a smoothing unit that smooths the rectified current and converts the rectified current to a current that corresponds to the capacitance of the electrode.